Method for determining chlorine gas released by anode of all-vanadium redox flow battery by alkali solution absorbing potassium iodide reduction ultraviolet-visible spectrophotometry and application

Abstract

This invention provides a method and its application for determining chlorine gas evolved at the anode of a vanadium redox flow battery using an alkaline absorption potassium iodide reduction ultraviolet-visible spectrophotometric method. The method includes the preparation of a standard working curve and the preparation and determination of the test solution. This invention selects iodide ions as the reducing agent, utilizing the oxidizing property of chlorine gas to oxidize the iodide ions and generate I3. ‑ Ions, and utilize I3 ‑ The light absorption properties of ions enable indirect determination of chloride ion content. The method described in this invention allows for qualitative and quantitative analysis of chlorine gas released from the anolyte during operation of a hydrochloric acid-based vanadium redox flow battery, enabling safe monitoring of the battery's operation. Furthermore, this invention can also be applied to the determination of chlorine content in the environment.

Description

Technical Field

[0001] This invention relates to chlorine determination technology, and more particularly to a method and application of alkaline absorption potassium iodide reduction ultraviolet-visible spectrophotometry for determining chlorine gas evolved at the anode of a vanadium redox flow cell. Background Technology

[0002] During the operation of a hydrochloric acid-based vanadium redox flow battery, when charged to a high state of charge (SOC), chloride ions in the anolyte may be oxidized to chlorine gas, which is then released. Chlorine gas is highly corrosive and can harm equipment and personnel; furthermore, it has high oxidizing properties and poses a risk of flash explosion when it encounters reducing gases such as hydrogen. Therefore, it is necessary to establish a method to verify whether chlorine gas is generated during experiments or battery operation and to perform quantitative analysis.

[0003] The environmental standard recommends the methyl orange spectrophotometric method for detecting chlorine content. This method works by reacting chlorine gas with an acidic solution containing potassium bromide and methyl orange. The chlorine oxidizes bromide ions to bromine, which then reduces the red color of the methyl orange solution in the acidic solution. The degree of fading is determined spectrophotometrically to ascertain the chlorine content. However, this method has several drawbacks: firstly, the absorption solution is acidic, which affects the efficiency of the chlorine absorption reaction and thus the accuracy of the detection; secondly, literature reports that this method has relatively low sensitivity, with a detection limit of 0.03 mg / m³ in ion chromatography. 3 The detection limit of this method is 0.19 mg / m³. 3 .

[0004] Another traditional method for chlorine detection involves absorbing HCl from the waste gas with a saturated NaCl solution, followed by absorbing the chlorine with a KOH absorbent of a certain concentration, causing a disproportionation reaction. A portion of the chlorine that forms hypochlorite is reduced to chloride ions by sodium thiosulfate and then quantitatively analyzed together with the chloride ions generated in the disproportionation reaction using an ion chromatograph. The chlorine concentration is then calculated. This method also has certain drawbacks. Firstly, since the target gas is chloride ions, pretreatment is required to separate HCl from the sample gas. Secondly, the equipment and maintenance costs are high, as are the consumable costs, resulting in high sample testing costs.

[0005] Current chlorine detection methods all have varying degrees of drawbacks, so there is an urgent need for a quantitative chlorine analysis method suitable for the operation of hydrochloric acid-based vanadium redox flow batteries. Summary of the Invention

[0006] The purpose of this invention is to address the numerous problems existing in traditional quantitative chlorine analysis methods by proposing a method for determining chlorine gas evolved at the anode of a vanadium redox flow battery using alkaline absorption potassium iodide reduction ultraviolet-visible spectrophotometry. This method enables qualitative and quantitative analysis of chlorine evolved in the anode solution during the operation of a hydrochloric acid-based vanadium redox flow battery, achieving safe monitoring of the battery's operation. Furthermore, this invention can also be applied to the determination of chlorine content in the environment.

[0007] To achieve the above objectives, the technical solution adopted by this invention is: a method for determining chlorine gas evolved at the anode of a vanadium redox flow battery using alkaline absorption of potassium iodide reduction ultraviolet-visible spectrophotometry, comprising the following steps:

[0008] Step 1: Creating the Standard Working Curve

[0009] Transfer a series of volumes of iodine standard solution into N brown containers containing sodium hydroxide solution, add excess potassium iodide solution to each, rinse with a small amount of water and shake well, where N is greater than or equal to 5; after reacting for 2-5 minutes, add concentrated hydrochloric acid to adjust the solution to acidity (pH 1-4) to improve colorimetric stability; dilute to volume with water to obtain N test samples, let the test samples stand for 3-5 minutes, and use a UV-Vis spectrophotometer to measure the absorbance value of the solution at the characteristic spectral wavelength of the N test samples. The characteristic spectral wavelength is 287 nm or 350 nm. Plot a standard working curve with the molar concentration of iodine contained in the series of volumes of iodine standard solution as the ordinate and absorbance as the abscissa to obtain the linear relationship between the molar concentration of iodine and absorbance A. The amount of potassium iodide added is much greater than three times the amount of iodine added.

[0010] Step 2: Preparation and Determination of Test Solution

[0011] Taking advantage of the high density of chlorine, nitrogen gas is introduced into the reaction vessel to replace the volatile gas (containing chlorine). Chlorine is then collected by absorption with an alkaline solution to obtain the test solution. Water is added to dilute the solution to obtain a chlorine-containing absorbent. A certain volume of the chlorine-containing absorbent is transferred to a brown volumetric flask, excess potassium iodide solution is added, and the mixture is rinsed and shaken well. After reacting for 2-3 minutes, concentrated hydrochloric acid is added to make the solution acidic (pH 1-4) to improve colorimetric stability. The solution is then diluted to dilute the solution with water to obtain the test sample. After the test sample has stood for 3-5 minutes, it is sampled, and the absorbance at 350 nm is measured using a UV-Vis spectrophotometer. The absorbance value is substituted into the linear equation of the standard working curve to calculate the chlorine molar concentration. The total amount of chlorine in the container is calculated based on the volume transferred and the volume of the absorbent.

[0012] Furthermore, step 1, the creation of the standard working curve, includes the following steps:

[0013] Accurately transfer 0.5, 1, 2, 3, 4, and 5 mL of iodine standard solution (1 g / L) into 100 mL brown volumetric flasks. Rinse the flask mouth with a small amount of water, add excess potassium iodide solution, rinse with a small amount of water, and shake well. Let it react for 2-3 min, then add concentrated hydrochloric acid, dilute to volume, and let it stand for 3-5 min. Use a 1 cm cuvette to measure the absorbance of the test solution at a wavelength of 350 nm or 287 nm. At the same time, prepare a blank. Plot the standard working curve with absorbance as the abscissa and iodine content (mol / L) as the ordinate to obtain formula (5); as shown in formulas (1) and (2): one chlorine molecule reacts with two iodide ions to generate one I3. - Ions; as shown in formula (3), an iodine molecule reacts with an iodide ion to produce an I3 ion. - Since ions are present, the standard working curve plotted from the iodine standard solution can be directly used to calculate the corresponding chlorine content.

[0014] C X =K×A+b...........(5)

[0015] C x —Iodine content, in moles per liter, mol / L;

[0016] A – Absorbance value of the test solution;

[0017] K—Slope of the standard working curve;

[0018] b—Standard working curve intercept.

[0019] Furthermore, the preparation and standardization of the iodine standard solution (1 g / L) in step 1 includes the following steps:

[0020] To prepare the solution, weigh 3.0 g of solid iodine and dissolve it in a beaker containing 30 mL of anhydrous ethanol. Stir with a glass rod to ensure the iodine is fully dissolved. Then, pour the ethanol solution of iodine into a brown reagent bottle containing 3 L of water, sonicate for 5 min, and let stand for 24 h. After 24 h, filter the solution with filter paper to obtain a clear and transparent saturated iodine solution, which is then stored in a brown reagent bottle.

[0021] For standardization, accurately transfer volume V1 of iodine standard solution (1 g / L) with a pipette, add 50 mL of water, titrate with sodium thiosulfate standard titration solution (0.5 g / L) until light yellow, add 1 mL of starch indicator (1%), and titrate with sodium thiosulfate standard titration solution (0.5 g / L) until the blue color disappears. Record the titration volume V2, and calculate the iodine standard solution content according to formula (4).

[0022]

[0023] Test passed:

[0024] —Iodine standard solution concentration, in moles per liter, mol / L;

[0025] C NaS2O3 —The concentration of the sodium thiosulfate standard solution is expressed in moles per liter (mol / L).

[0026] V1 — Volume of iodine standard solution transferred, in milliliters (mL);

[0027] V2 — Volume of sodium thiosulfate standard solution consumed, in milliliters (mL).

[0028] Furthermore, step 2, test solution preparation and determination, includes the following steps:

[0029] 2.1 Preparation of test solution

[0030] Taking advantage of the high density of chlorine, the volatile gas (containing chlorine) in the reaction vessel is replaced by nitrogen gas passing through the top. Then, the chlorine is collected by absorbing it with alkaline solution to obtain the test solution. Water is added to make up the volume to obtain the chlorine-containing absorbent solution. The volume after making up the volume is V3.

[0031] 2.2 Determination of the test solution

[0032] Transfer a certain volume of V4 chlorine-containing absorbent solution into a brown volumetric flask, add a small amount of water to rinse the mouth of the flask, add excess potassium iodide solution, add a small amount of water to rinse and shake well. After reacting for 3-5 minutes, add about concentrated hydrochloric acid to adjust the solution to acidity (pH 1-4), make up to volume V5, shake well and let stand for a certain time. Use a 1cm cuvette to measure the absorbance value at a wavelength of 350nm, and make a blank at the same time; calculate the total amount of chlorine according to formula (6);

[0033] 2.3 Formula for calculating chlorine content (Cl2, mol):

[0034]

[0035] Test passed:

[0036] C Cl2 —The total amount of chlorine contained in the volatile gases, expressed in moles (mol).

[0037] A – Absorbance value of the test solution;

[0038] K—Slope of the standard working curve;

[0039] b—Standard working curve intercept;

[0040] V3 — Volume of chlorine absorption liquid at a fixed volume, in milliliters (mL);

[0041] V4 — Volume of absorbent solution taken, in milliliters (mL);

[0042] V5—The volume of the absorbent solution after the redox reaction is completed, in milliliters (mL);

[0043] 1000 – Conversion factor between milliliters and liters.

[0044] Furthermore, the alkaline solution is a sodium hydroxide solution.

[0045] Furthermore, the concentration of the sodium hydroxide solution is 0.5-1.0 mol / L.

[0046] Furthermore, the reaction vessel is an anode of a vanadium redox flow battery.

[0047] Another objective of this invention is to disclose the application of a method for determining chlorine gas generated at the anode of a vanadium redox flow battery using alkaline absorption potassium iodide reduction ultraviolet-visible spectrophotometry in the fields of hydrochloric acid system vanadium redox flow batteries and chlorine content determination in the environment.

[0048] This invention relates to a method for determining chlorine gas evolution at the anode of a vanadium redox flow battery using alkaline absorption and potassium iodide reduction ultraviolet-visible spectrophotometry. Iodide ions are selected as the reducing agent, and the oxidizing properties of chlorine gas are used to oxidize the iodide ions to generate I₃. - Ions, and utilize I3 - The light absorption properties of ions enable the indirect determination of chloride ion content. The specific working principle is as follows:

[0049] This invention utilizes the high density of chlorine gas to introduce nitrogen gas into the reaction vessel to replace volatile gases (containing chlorine gas) and collect them by absorption with alkaline solution (sodium hydroxide solution). After being absorbed, the chlorine gas will undergo a disproportionation reaction to generate hypochlorite ions, as shown in formula (1).

[0050] Cl2+2OH-=Cl-+ClO-+H2O......................(1)

[0051] Adding an appropriate amount of potassium iodide solution to the absorption solution causes hypochlorous acid in the solution to undergo a redox reaction with potassium iodide to generate I3. - It has good light absorption properties and can be used for ultraviolet-visible spectrophotometry. The reaction is shown in formula (2).

[0052]

[0053] As shown in formula (3), one iodine molecule and one chlorine molecule react with iodide ions to produce one I3 molecule. - In this invention, iodine standard solution is used instead of chlorine standard solution to prepare a standard working curve. The I3 generated in the quantitative redox reaction of potassium iodide and hypochlorous acid is determined using a UV-Vis spectrophotometer. -The method analyzes and calculates the chlorine content in the absorbing liquid by measuring changes in absorbance intensity at characteristic spectra, and then calculates the total chlorine content in the container based on the volume of the absorbing liquid and the volume taken out. This method has high detection sensitivity and has a very broad application prospect in the operation monitoring of vanadium redox flow batteries. This method can also be applied to the determination of chlorine content in the environment.

[0054]

[0055] This invention discloses a method for determining chlorine gas evolved at the anode of a vanadium redox flow battery using alkaline absorption and potassium iodide reduction ultraviolet-visible spectrophotometry. This method utilizes the high density of chlorine gas. Nitrogen gas is introduced to displace the chlorine gas in the container, and the gas is collected by absorption with an alkaline solution (sodium hydroxide solution). After absorption, the chlorine gas undergoes a disproportionation reaction to generate hypochlorite. An appropriate amount of potassium iodide solution is added to the absorption solution, where the hypochlorite ions react with the potassium iodide in a redox reaction to generate I₃. - It exhibits excellent light absorption characteristics and can be used for ultraviolet-visible spectrophotometric determination. Specifically, the method described in this invention has the following advantages compared with existing technologies: The application of this invention enables qualitative and quantitative analysis of chlorine gas evolved from the anolyte during the operation of a chlorine-based vanadium redox flow battery, achieving safe monitoring of the operation of a hydrochloric acid-based vanadium redox flow battery. Simultaneously, this invention can also be applied to the determination of chlorine content in the environment. Attached Figure Description

[0056] Figure 1 The working curve shows the linear relationship between concentration and absorbance. Detailed Implementation

[0057] The present invention will be further described below with reference to the embodiments:

[0058] Example 1

[0059] 1. Experimental reagents

[0060] 1.1 Potassium dichromate standard reagent: Dry in an oven at 120℃ for 2 hours, then cool to room temperature.

[0061] 1.2 Sodium thiosulfate solution (5g / L): Dissolve 5g sodium thiosulfate pentahydrate and 0.04g sodium carbonate in distilled water, make up to 1L in a volumetric flask, store in a brown reagent bottle to prevent decomposition, and titrate with potassium dichromate after 2-3 days.

[0062] 1.3 Sodium thiosulfate solution (0.5 g / L): Transfer 25 mL of standardized sodium thiosulfate solution (5 g / L) to a 250 mL volumetric flask and dissolve.

[0063] 1.3 Potassium iodide solution (30g / L): Weigh 8.3g of potassium iodide solid and dissolve it in a beaker containing 150mL of water. Once completely dissolved, dilute to a volumetric flask of 250mL.

[0064] 1.4 Hydrochloric acid solution (2 mol / L): Measure 17 mL of hydrochloric acid and make up to 100 mL in a volumetric flask.

[0065] 1.5 Starch indicator (1%): Weigh 1g of soluble starch, mix with a small amount of water to form a paste, then add boiling water to dissolve it completely. After cooling, bring the volume to a final volume. (For long-term storage, add 0.1g of salicylic acid or 0.4g of zinc chloride).

[0066] 1.6 Iodine solution (1 g / L): Weigh 3.0 g of solid iodine and dissolve it in a beaker containing 30 mL of anhydrous ethanol. Stir with a glass rod until the iodine is fully dissolved. Then pour the iodine ethanol solution into a brown reagent bottle containing 3 L of water, sonicate for 5 min, and let stand for 24 h. After 24 h, filter with filter paper to obtain a clear and transparent saturated iodine solution, which is stored in a brown reagent bottle.

[0067] 2. Experiment Content

[0068] 2.1 Standardization of sodium thiosulfate: Accurately weigh 0.02 g of potassium dichromate and place it in a 250 mL iodine flask. Add 10-20 mL of water to dissolve it. Add 10 mL of potassium iodide solution (30 g / L) and 2 mL of hydrochloric acid (2 mol / L). Mix thoroughly and dissolve. Cover the flask to prevent iodine from evaporating. Place it in the dark for five minutes. Add 30 mL of water to dilute it. Titrate with sodium thiosulfate solution (5 g / L) until a light yellow-green color appears. Add 1 mL of starch indicator (1%) and continue titrating the sodium thiosulfate solution until the blue color disappears. Record the titration volume.

[0069] 2.2 Standardization of iodine standard solution: Accurately transfer 25 mL of iodine standard solution (1 g / L) into a pipette, add 50 mL of water, titrate with sodium thiosulfate solution (0.5 g / L) until the solution turns pale yellow, add 1 mL of starch indicator (1%), and titrate again with sodium thiosulfate solution (0.5 g / L) until the blue color disappears. Record the titration volume.

[0070] 2.3 Standard Curve Plotting: Accurately transfer 0.5, 1, 2, 3, 4, and 5 mL of iodine standard solution (1 g / L) into 100 mL brown volumetric flasks. Rinse the flask mouth with a small amount of water, add 5 mL of potassium iodide solution (30 g / L), rinse with a small amount of water, and shake well. Let it react for 3 min, then add 1 mL of hydrochloric acid (2 mol / L), dilute to volume, shake well, and let stand for 5 min. Simultaneously, prepare a blank and perform colorimetric analysis at a wavelength of 350 nm. Plot the standard curve with absorbance as the abscissa and iodine content (mol / L) as the ordinate.

[0071] 2.4 Sample solution determination: Transfer 0.2 mL of the electrolytic anode CVE electrolytic absorption solution into a 100 mL brown volumetric flask, add a small amount of water to rinse the mouth of the flask, add 5 mL of potassium iodide solution (3.1.2), add a small amount of water to rinse and shake well, react for 3 min, then add 1 mL of hydrochloric acid (2 mol / L), make up to volume, shake well and let stand for 5 min, and at the same time prepare a blank, and perform colorimetric analysis at a wavelength of 350 nm.

[0072] 2.5 Calculation Formula

[0073] 2.5.1 Sodium thiosulfate solution concentration C NaS2O3 (mol / L) calculation formula:

[0074]

[0075] Test passed:

[0076] C NaS2O3 —Sodium thiosulfate solution concentration, in mol / L;

[0077] m — the mass of potassium dichromate weighed, in grams;

[0078] M – Molecular weight of potassium dichromate, in g / mol;

[0079] V0 — Volume of sodium thiosulfate solution consumed, in mL.

[0080] 2.5.2 Iodine solution concentration C I2 (mol / L) calculation formula:

[0081]

[0082] Test passed:

[0083] C I2 —I₂ solution concentration, in mol / L;

[0084] C NaS2O3 —Sodium thiosulfate solution concentration, in mol / L;

[0085] V1 — Volume of iodine standard solution transferred, in milliliters (mL);

[0086] V2 — Volume of sodium thiosulfate standard solution consumed, in milliliters (mL).

[0087] 2.5.3 Chlorine content C Cl2 (mol) calculation formula:

[0088]

[0089] Test passed:

[0090] CCl2 —The total amount of chlorine contained in the volatile gases, expressed in moles (mol).

[0091] A – Absorbance value of the test solution;

[0092] K—Slope of the standard working curve;

[0093] b—Standard working curve intercept;

[0094] V3 — Volume of chlorine absorption liquid at a fixed volume, in milliliters (mL);

[0095] V4 — Volume of absorbent solution taken, in milliliters (mL);

[0096] V5—The volume of the absorbent solution after the redox reaction is completed, in milliliters (mL);

[0097] 1000 – Conversion factor between milliliters and liters.

[0098] 3. Data Processing

[0099] Table 1. Iodine standard solution calibration data and analysis

[0100]

[0101] Table 2 Test results of chlorine absorbent liquid samples

[0102]

[0103] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for determining chlorine gas evolved at the anode of a vanadium redox flow cell using alkaline absorption and potassium iodide reduction ultraviolet-visible spectrophotometry, characterized in that... Includes the following steps: Step 1: Creating the Standard Working Curve A series of volumes of iodine standard solution were transferred to N brown containers containing sodium hydroxide solution. Excess potassium iodide solution was added to each container, and a small amount of water was added to rinse and shake well, where N is greater than or equal to 5. After reacting for 2-5 minutes, concentrated hydrochloric acid was added to adjust the solution to acidity to improve color development stability. The solution was diluted with water to obtain N test samples. After the test samples were allowed to stand for 3-5 minutes, the absorbance values ​​of the solution at the characteristic spectral wavelength of the N test samples were measured using a UV-Vis spectrophotometer. The characteristic spectral wavelength was 287 nm or 350 nm. A standard working curve was plotted with the molar concentration of iodine contained in the series of volumes of iodine standard solution as the ordinate and the absorbance as the abscissa to obtain the linear relationship between the molar concentration of iodine and the absorbance A. The amount of potassium iodide added was much greater than three times the amount of iodine added. Step 2: Preparation and Determination of Test Solution Taking advantage of the high density of chlorine, nitrogen gas is introduced into the reaction vessel to replace volatile gases. Chlorine is then collected by absorption with an alkaline solution to obtain the test solution. Water is added to dilute the solution to obtain a chlorine-containing absorbent. A certain volume of the chlorine-containing absorbent is transferred to a brown volumetric flask, excess potassium iodide solution is added, a small amount of water is added for rinsing and shaking, and the mixture is allowed to react for 2-3 minutes. Concentrated hydrochloric acid is then added to make the solution acidic, improving colorimetric stability. The solution is then diluted to dilute the solution with water to obtain the test sample. After the test sample has stood for 3-5 minutes, it is sampled, and the absorbance at 350 nm is measured using a UV-Vis spectrophotometer. The absorbance value is substituted into the linear equation of the standard working curve to calculate the chlorine molar concentration. The total amount of chlorine in the container is calculated based on the volume transferred and the volume of the absorbent.

2. The method for determining chlorine gas evolution at the anode of a vanadium redox flow cell using alkaline absorption and potassium iodide reduction ultraviolet-visible spectrophotometry according to claim 1, characterized in that, Step 1, creating the standard working curve, includes the following steps: Accurately transfer 0.5, 1, 2, 3, 4, and 5 mL of iodine standard solution into 100 mL brown volumetric flasks, add a small amount of water to rinse the mouth of the flask, add excess potassium iodide solution, add a small amount of water to rinse and shake well, react for 2-3 min, then add concentrated hydrochloric acid, make up to volume, let stand for 3-5 min, and then use a 1 cm cuvette to measure the absorbance of the test solution at a wavelength of 350 nm or 287 nm. At the same time, make a blank, plot the standard working curve with absorbance as the abscissa and iodine content as the ordinate, and obtain formula (5). C X = K x A + b (5) C x —Iodine content, in moles per liter, mol / L; A – Absorbance value of the test solution; K—Slope of the standard working curve; b—Standard working curve intercept.

3. The method for determining chlorine gas evolution at the anode of a vanadium redox flow cell using alkaline absorption potassium iodide reduction ultraviolet-visible spectrophotometry according to claim 1 or 2, characterized in that... The preparation and standardization of the iodine standard solution in step 1 includes the following steps: To prepare the solution, weigh 3.0 g of solid iodine and dissolve it in a beaker containing 30 mL of anhydrous ethanol. Stir with a glass rod to ensure the iodine is fully dissolved. Then, pour the ethanol solution of iodine into a brown reagent bottle containing 3 L of water, sonicate for 5 min, and let stand for 24 h. After 24 h, filter the solution with filter paper to obtain a clear and transparent saturated iodine solution, which is then stored in a brown reagent bottle. For standardization, accurately transfer volume V1 of iodine standard solution with a pipette, add 50 mL of water, titrate with sodium thiosulfate standard solution until light yellow, add 1 mL of starch indicator, and titrate with sodium thiosulfate standard solution until the blue color disappears. Record the titration volume V2, and calculate the iodine standard solution content according to formula (4). Test passed: —Iodine standard solution concentration, in moles per liter, mol / L; C NaS2O3 —The concentration of the sodium thiosulfate standard solution is expressed in moles per liter (mol / L). V1 — Volume of iodine standard solution transferred, in milliliters (mL); V2 — Volume of sodium thiosulfate standard solution consumed, in milliliters (mL).

4. The method for determining chlorine gas evolution at the anode of a vanadium redox flow cell using alkaline absorption and potassium iodide reduction ultraviolet-visible spectrophotometry according to claim 1, characterized in that... Step 2, reagent preparation and determination, includes the following steps: 2.1 Preparation of test solution Taking advantage of the high density of chlorine, the volatile gases in the reaction vessel are replaced by nitrogen gas flowing through the top, and then chlorine is collected by absorbing it with alkaline solution to obtain the test solution. Water is added to make up the volume to obtain a chlorine-containing absorbent solution with a volume of V3 after making up the volume. 2.2 Determination of the test solution Transfer a certain volume of V4 chlorine-containing absorbent solution into a brown volumetric flask, add a small amount of water to rinse the mouth of the flask, add excess potassium iodide solution, add a small amount of water to rinse and shake well. After reacting for 3-5 minutes, add about concentrated hydrochloric acid to adjust the solution to acidity, make up to volume V5, shake well and let stand for a certain time. Use a 1cm cuvette to measure the absorbance value at a wavelength of 350nm, and make a blank at the same time; calculate the total amount of chlorine according to formula (6); 2.3 Formula for calculating chlorine content (Cl2, mol): Test passed: C Cl2 —The total amount of chlorine contained in the volatile gases, expressed in moles (mol). A – Absorbance value of the test solution; K—Slope of the standard working curve; b—Standard working curve intercept; V3 — Volume of chlorine absorption liquid at a fixed volume, in milliliters (mL); V4 — Volume of absorbent solution taken, in milliliters (mL); V5—The volume of the absorbent solution after the redox reaction is completed, in milliliters (mL); 1000 – Conversion factor between milliliters and liters.

5. The method for determining chlorine gas evolution at the anode of a vanadium redox flow cell using alkaline absorption of potassium iodide reduction ultraviolet-visible spectrophotometry according to claim 1, characterized in that... The alkaline solution is a sodium hydroxide solution.

6. The method for determining chlorine gas evolution at the anode of a vanadium redox flow cell using alkaline absorption potassium iodide reduction ultraviolet-visible spectrophotometry according to claim 5, characterized in that... The concentration of the sodium hydroxide solution is 0.5-1.0 mol / L.

7. The method for determining chlorine gas evolution at the anode of a vanadium redox flow cell using alkaline absorption and potassium iodide reduction ultraviolet-visible spectrophotometry according to claim 1, characterized in that... The reaction vessel is an anode of a vanadium redox flow battery.

8. The method for determining chlorine gas generated at the anode of a vanadium redox flow battery by alkaline absorption of potassium iodide reduction ultraviolet-visible spectrophotometry according to any one of claims 1-7, is applicable in the field of hydrochloric acid system vanadium redox flow batteries and in the field of chlorine content determination in the environment.

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